(a) Field of the Invention
The present invention relates to an automatic transmission for a vehicle and more particularly, to a planetary gear train of an automatic transmission for a vehicle that improves a power delivery performance and enhances fuel consumption by implementing at least forward nine-speed with a reduced configuration and reduces running noise of the vehicle by utilizing a driving point in a low rotation speed range of an engine.
(b) Description of the Related Art
Generally, in an automatic transmission field research on a multistage of a gear shift stage has been conducted to enhance fuel consumption and to maximize drivability of a vehicle. In particular, an increase of the cost of oil price has resulted in requirements to enhance fuel consumption of a vehicle. Accordingly, research that reduces a weight and enhances fuel consumption of an engine has been conducted to reduce the size of the engine. For example research on an automatic transmission has been conducted to simultaneously secure drivability and fuel consumption competitive power through a multistage of a gear shift stage. However, in the automatic transmission, as a number of gear shift stage increases, the internal component number of the planetary gear set number increases. In other words, the length of the transmission increases and a mounting ability, a production cost, a weight, and power delivery efficiency may be reduced.
Therefore, in the automatic transmission, to increase a fuel consumption of the automatic transmission, an enhancement effect through a multistage of a gear shift stage requires development of a planetary gear train that induces maximum efficiency with the minimal number of required components. Accordingly, an automatic transmission implements a shift of 8-speed or greater to be mounted within a vehicle. Research and development of a planetary gear train that implements a gear shift stage of 8-speed or greater has been continuously required.
However, a general 8-speed or more of automatic transmission is typically formed with three or four planetary gear sets and five or six control elements (e.g., friction element). In other words the total length is increased and may degrade a mounting ability. To form a gear shift stage of an automatic transmission in a multistage, a double row structure that disposes a planetary gear set on a planetary gear set has been adapted or a dog clutch may be applied instead of a wet control element. However, structure may be limited and a shift feel may be degraded due to application of the dog clutch.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.